The layout markers now on the market contain an ink composition based on toluol or, in particular xylol, with an oilsoluble dye, or dye soluble in organic solvents. Such markers are quite usable, because they are available in various colors; also, relatively large surface areas can be covered with them, without causing rippling of the drafting material. However, xylol and toluol both have grave disadvantages in terms of health: The solvent vapors have a penetrating odor, and hence often cause nausea or dizziness, and lead to a severe irritation of the mucous membranes, especially in the nose, mouth and throat, as well as in the eyes. Moreover, many people have an allergic reaction (skin inflammation) to these solvents. Pathological changes in the bone marrow can even occur if xylol vapors are inhaled over relatively long periods of time, especially with occupational use of such markers.
German Examined Application DE-AS 23 35 955, in order to overcome this problem, proposes an ink composition for a marker which contains certain modified dyes as well as resin-like binders, in an alicyclic hydrocarbon solvent. However, such ink compositions are not entirely satisfactory from the user's standpoint, because the markers filled with them rapidly dry out if the solvent is highly volatile; on the other hand, if solvents of higher boiling points are used, the ink dries too slowly on the drawing material. The complexity of production is a further consideration, because dyes available on the market cannot be used as is, but instead must be chemically modified first.
A jet printing ink known from German Patent 29 24 861 contains a dye or pigment in a liquid vehicle, which comprises a monovalent or multivalent alcohol or an alkanolamine, a nitrogen-containing five-member ring ketone or a lower mono- or dialkyl ether of an alkylene glycol, optionally water, and an aliphatic carbonic acid ester. The dye may be a water-soluble or water-insoluble dye, or pigments that are dispersed in the liquid vehicle can be used. Such jet printing inks are predominantly unsuitable for use in a marker or felt tip pen.
The same is true for the jet printing inks of unexamined German Application DE-OS 36 26 567, comprising a slightly water-soluble dye, water and an organic solvent having a boiling point of more than 120.degree. C, which primarily means certain ethers. For the purposes of the invention, the low solubility of the dye in water is especially disadvantageous, since as a rule this solubility decreases still further with the admixture of the organic solvent.